1. Field of the Invention
This invention relates to nondestructive testing apparatus, more particularly, to a measuring probe used to inspect tubular members and passageways.
2. Prior Art
It is known in the art to have remote sensors, or probes, traveling in tubular members, such as are found in steam generators and heat exchangers, to inspect the integrity of such tubes and conduits when human access is restricted. Generally, a testing probe is delivered internal the conduits by means of a positioning shaft to which it is attached. As the shaft impels the probe into the conduit, the probe measures the host conduit along its length, or longitudinally, transmitting probe measurement data out of the conduit through cables carried in a duct within the shaft. An eddy current probe is one such remote sensor commonly employed in the inspection of conduits.
Eddy current probes operate by coils alternating an electromagnet field into a conduit as it travels within the conduit and receiving electromagnetic returns from the conduit. In interacting with the conduit structure, the field is able to locate defects by recognizing anomalies, such as disbonds, bubbles, cracks, corrosion, delaminations, thickness variation, and the like.
At least one eddy current test coil is commonly mounted circumferentially around the probe. In this configuration, it is required that the probe be aligned centrally on the conduit axis to insure a viable and reproducible measurement. It is known to have resilient centering feet about the eddy current coils located in a probe body to achieve the desired axial position of the probe test coils. As the probe travels through the conduit, the probe rides on the centering feet that slide along the conduit inner surface, thus directing the probe and assuring a constant distance of the coils from the conduit. In this operational mode, the sliding centering feet become abraded through repeated use.
To the degree they are abraded, the eddy current probe is off center and produces a degraded measurement. After a period of use the probe becomes unreliable and therefore unusable due to the abraded centering feet; the entire probe must be discarded even while the balance of the probe is fully usable. With the considerable use, complexity and expense of eddy current probes, it is desirable to have an eddy current probe that does not need to be fully discarded when its centering feet become abraded.
It is thus the object of the present invention to provide an eddy current probe with replaceable centering feet.